Its other name is the social fairy wrasse, and the arithmetic of that is worth spelling out.
These fish live in harems: one male, several females, on a defined patch of slope. The male spends his day patrolling it, displaying at the females and driving off other males, and he is the only one breeding. Every female in the group is a fish that has not yet had the opportunity to become male.
When he dies the largest female starts changing within hours. Her behavior goes first - she begins patrolling and displaying before anything about her body has altered - and the color and the anatomy follow over the next days and weeks. The group barely pauses.
So a harem is not a male's collection. It is a queue, and the male at the front of it is the fish that got there first and is holding the position for as long as he can.
They live on mixed grass, sand and rubble slopes rather than on coral, which is the sort of in-between ground most divers cross without stopping, and they feed on zooplankton a little above the bottom.
The species. Cirrhilabrus rubriventralis Springer & Randall 1974 - rubrum. ETYFish
- males red above with a red belly and long trailing pelvic fins
- females smaller, plainer, orange-pink
- in small groups, one male among several females
- up to 7.5 cm
Why it's threatened
There are no known major threats to this species, although it is exploited in the aquarium trade.
Threat classification from the IUCN Red List.
